Basic question about sensitivity

Could impedance and sensitivity be getting mixed up somewhere?

@immatthewj Wrote:

 

Basic question about sensitivity

See article below:

Mike

I think, in general, the way you are looking at things with more sensitivity requiring more power is correct. I think Harbeth are somewhat of an anomaly.

Like all things audio, it depends. Recommended wpc amplification is a very open and unscientific… well recommendation. It can be as much marketing as a real requirment.

The nominal impedance of the Harbeth P3ESR XD is 6 ohms. Which they advertise as “easy to drive”, since many speakers with a sensitivity of 83 are very hard to drive, requiring a lot of power and having impedances dipping down to 2 ohms or lower. The impedance is a measure of easily electrons flow through… and at 2 ohms they flow easily, and if the amp can’t produce tremendous current then it runs out of power.

Also speakers are rated at nominal impedance… because they vary across the audio spectrum. So, some speakers dip to 1 ohm, then go to 8 or more ohms… the nominal impedance could be almost any thing. The electrical characteristics are so much more complicated that these two parameters show, they tell very little with certainty.

A better measure of amps is current… and for speakers the lower the impedance the more current they need to perform properly.

I never look at the power requirements and when purchasing solid state amps I have generally purchased amps of far more than the recommended power rating because they tend to sound better. Tube amps are not nearly as likely to show that they are running low on power.

I choose amps for their character and make sure they have lots of power… regardless of speaker. If you choose Harbeth, you are choosing a specialty speaker and should research amplification carefully.

Higher efficiency = easier to drive.

Higher sensitivity = more output at given voltage.

When the speaker is 8 Ohms, efficiency and sensitivity are the same.

Here’s a common example: Many mid woofers come in 8 ohm and 4 ohm versions. Nearly identical in all other aspects besides the impedance curves. The 8 Ohm version produces 87 dB at 2.83 V. That is, 87 db @ 1 Watt. The 4 ohm speaker produces 90 dB @ 2.83V, but since it has 2x the current it is 90 dB @ 2 Watts.

Generally speaking though, it’s hard to find high sensitivity speakers ( 97 dB or higher) that are not also benign impedance (8 Ohms or better).

To make it easier on you, keep an eye on "minimum impedance" not "nominal impedance."  Higher minimum is (generally) easier to drive, and the sensitifity/efficiency will tell you how loud it will get with your amp.

Higher efficiency = easier to drive.

Higher sensitivity = more output at given voltage.

When the speaker is 8 Ohms, efficiency and sensitivity are the same.

@erik_squires , thank you. The Monitor Audio Gold 300 5G (sensitivity 90) minimum impedance is stated to be 3.5 ohms, which would then explain the need for more power.

@ghdprentice , thank you; I am curious, when you refer to the Harbeth as a "specialty speaker," what do you mean by that.

Thank you for responding @ellajeanelle , no, I wasn’t confusing impedance with sensitivity; however I was not understanding the relationship between the two.

@ditusa , thank you for the link. I read through it quite quickly and it does appear to be quite informative. I am going to give it a careful thorough read.